The aim of the project was to demonstrate the advantages and disadvantages of new types of fuel and to develop a method in which detailed knowledge of the composition of a newly developed fuel is sufficient to assess its suitability for aviation. The project first worked through the physical and chemical principles of fuel behaviour and then investigated the effects of fuels on the entire aircraft system. The focus was on safety and environmentally relevant sub-processes. A reduction in the proportion of aromatics, for example, significantly reduces soot emissions, but also harbours the risk of lower material compatibility.
In Jetscreen, a two-stage process was developed in collaboration with the National Jet Fuels Combustion Programme (NJFCP). First, the fuel composition is analysed in the laboratory using qualitative and quantitative two-dimensional gas chromatography GCxGC and trace component analysis. Then, in a second step, selected properties of the fuel candidate are compared with the properties of products from already approved production pathways. The SimFuel database, which was also developed as part of the project, is used for this, incorporating models and data from several research institutions and companies involved in the project. It takes into account all the correlations that were analysed in the project.
The aviation industry's evaluation and qualification process for synthetic aviation fuel components, which is described in ASTM D4054 and other standards, can involve up to four test stages, two research reports and three rounds of approval. It is so complex that it can take several years and is associated with considerable costs for all parties involved. The project quickly highlighted the need for early, cost-effective and rapid prescreening techniques outside of the formal ASTM D4054 approval and evaluation process - particularly with regard to evaluating the functionality of aircraft combustion chambers, which are among the most complex tests in the entire evaluation process. Methods were required that could provide a manufacturer with information at an early stage as to whether their fuel would meet the specifications after completion of the ASTM D4054 evaluation process.
"We have developed a whole range of modelling tools that can be used to predict the behaviour of fuels based solely on information about the fuel composition," says Rauch. "These can now be used for the rapid screening and evaluation of new fuel candidates and to support the design of fuel-optimised aircraft and engines." The results of the prescreening do not replace the approval, but rather enable an early assessment of whether serious problems could arise during the tests as part of the formal approval process. This helps SAF developers to make early decisions regarding the composition or production processes. This increases the chances of later approval in both fast track and standard approvals. Prescreening also makes a significant contribution to reducing development costs.